Oviposition Behaviour in the Two Strains of the Rice Weevil, Calandra Oryzae Linn. (Coleopt., Curculionidae)

ABSTRACT A knowledge of the biotic potential of an insect population, i.e. of its rate of multiplication under various conditions, is of obvious importance in the case of grain-infesting insects. Such knowledge is available for very few species, for its computation requires exact information of certain biotic constants (Chapman & Baird, 1934) which can be determined only by protracted experiment. Not the least important of these is one which is a function of the fertility and rate of oviposition, and the primary aim of the present investigation has been to obtain information on this subject for the rice weevil, Calandra oryzae. Previous work on oviposition has frequently fallen short of requirement for several reasons. Where full-scale experiments have been carried out (e.g. Kunike (1936) and Lavrekhin (1937)), the control of environmental conditions has been too inadequate for the results to have any great value. Where a more rigid control has been attempted short-term experiments on rates of oviposition have usually been conducted (e.g. MacLagen & Dunn (1936), Crombie (1942), Richards and his co-workers (1944,1947)), and not infrequently selected females have been employed. The results, in consequence, though of value in other directions, are seldom if ever a reliable index of total fertility and throw little light on the general pattern of oviposition. Only in the cases of C. granaria (Eastham & McCully, 1943) and the small race of C. oryzae (Birch, 1945 a) have full data been obtained under adequately controlled conditions. In C. oryzaeRichards (1944) has demonstrated that there are two very distinct strains which differ principally in size, and one of these, the small strain, has already been the subject of full investigation (Birch, 1945 a, b). In the present work, there-fore, attention has been mainly directed towards the behaviour of the large strain, a limited number of parallel experiments being carried out with the small weevil for comparative purposes.